Integrated process for the production of vinyl acetate from acetic acid via ethylene

ABSTRACT

This invention provides an integrated two stage economical process for the production of vinyl acetate monomer (VAM) from acetic acid in the vapor phase. First, acetic acid is selectively hydrogenated over a hydrogenating catalyst composition to form ethylene either in a single reactor zone or in a dual rector zone wherein the intermediate hydrogenated products are either dehydrated and/or cracked to form ethylene. In a subsequent second stage so formed ethylene is reacted with molecular oxygen and acetic acid over a suitable catalyst to form VAM. In an embodiment of this invention reaction of acetic acid and hydrogen over a hydrogenation catalyst and subsequent reaction over a dehydration catalyst selectively produces ethylene, which is further mixed with acetic acid and molecular oxygen and reacted over a supported palladium/gold/potassium catalyst.

This application is a continuation of U.S. application Ser. No.12/291,949, filed on Nov. 14, 2008, the entire content and disclosure ofwhich is hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates generally to an integrated process for theproduction of vinyl acetate monomer (VAM) from the reaction of aceticacid and ethylene. More specifically, the present invention relates toan integrated process in which acetic acid is converted to ethylene in afirst reaction zone with the ethylene further reacted with additionalacetic acid in another reaction zone to form VAM. The present inventionalso relates to an integrated process including hydrogenating aceticacid utilizing a first catalyst composition in a first reaction zone anddehydrating or cracking hydrogenated intermediates with a secondcatalyst in a second reaction zone to form ethylene. The ethylene fromthe second reaction zone is reacted with additional acetic acid in athird reaction zone to produce VAM.

BACKGROUND

There is a long felt need for an economically viable process tomanufacture VAM from acetic acid without utilizing independently sourcedethylene. VAM is an important monomer in the production of polyvinylacetate and polyvinyl alcohol products among other important uses. Dueto fluctuating natural gas and crude oil prices contributing tovariations in the cost of conventionally produced petroleum or naturalgas-sourced ethylene, an important feedstock used in the manufacture ofVAM, the need for alternative cost-effective sources of ethylene inorder to produce VAM becomes all the greater.

It has now been found that VAM can be produced without utilizingindependently sourced ethylene. For example, it is well known thatsynthesis gas can be reduced to methanol, which is in fact one preferredway to manufacture methanol. Methanol thus formed can then be convertedselectively to acetic acid under catalytic carbonylation conditionswhich is a preferred process for the manufacture of acetic acid. Theacetic acid thus formed then can be selectively converted to ethyleneunder suitable catalytic conditions. Although there are no knownpreferred processes for such a conversion, the prior art does providecertain processes for such a conversion of acetic acid to ethylenealbeit at low conversions and yields thus making it industriallyunsuitable.

For instance, it has been reported that ethylene can be produced fromvarious ethyl esters in the gas phase in the temperature range of150-300° C. over zeolite catalysts. The types of ethyl esters that canbe employed include ethyl esters of formic acid, acetic acid andpropionic acid. See, for example, U.S. Pat. No. 4,620,050 to Cognion etal., where selectivity is reported to be acceptable.

U.S. Pat. No. 4,270,015 to Knifton describes obtaining ethyleneinvolving a two-step process in which a mixture of carbon monoxide andhydrogen (commonly known as synthesis gas (syngas)) is reacted with acarboxylic acid containing 2 to 4 carbon atoms to form the correspondingethyl ester of said carboxylic acid which is subsequently pyrolyzed in aquartz reactor at elevated temperatures in the range of about 200° to600° C. to obtain ethylene.

U.S. Pat. No. 4,399,305 to Schreck describes obtaining high purityethylene from ethyl acetate employing a cracking catalyst composed of aperfluorosulfonic acid resin commercially sold under the trademarkNAFION® by E.I. DuPont de Nemours & Co.

Once ethylene has been produced, further processing with acetic acid isrequired for conversion to VAM as demonstrated in U.S. Pat. No.6,696,596 to Herzog et al., incorporated herein by reference in itsentirety, which indicates that it is well known to manufacture VAM in areaction in the gas phase with acetic acid and oxygen or oxygencontaining gasses over fixed-bed catalysts.

Additional examples of the manufacture of VAM from ethylene and aceticacid are set forth in U.S. Pat. No. 6,040,474 to Jobson et al. whichdescribes the manufacture of acetic acid and/or vinyl acetate using tworeaction zones wherein the first reaction zone comprises ethylene and/orethane for oxidation to acetic acid with the second reaction zonecomprising acetic acid and ethylene with the product streams beingsubsequently separated thereby producing vinyl acetate. See U.S. Pat.No. 6,476,261 to Ellis et al. which describes an oxidation process forthe production of alkenes and carboxylic acids such as ethylene andacetic acid which are reacted to form vinyl acetate demonstrating thatmore than one reaction zone can be used to form the vinyl acetate.

From the foregoing it is apparent that existing processes do not havethe requisite selectivity to ethylene nor does the existing art indicatestarting materials other than acetic acid which are expensive and/orintended to produce products other than ethylene.

The present invention utilizes ethylene derived from acetic acid to makeVAM in an integrated process, providing alternate synthetic routes whichmay be utilized for more cost effective production.

SUMMARY OF THE INVENTION

It has now been unexpectedly found that VAM can be produced on anindustrial scale involving an integrated process by which ethylene isproduced from acetic acid with high selectivity and yield, which isconverted to VAM in a subsequent step. VAM formation is referred to as“stage 2” below for convenience, while ethylene production is referredto as “stage 1”. Each of these stages, especially stage 1 can be carriedout in more than one reactor, if so desired, as will become apparentfrom the discussion which follows.

With high selectivity and yield it is now possible to produce VAMeconomically in two stages from acetic acid as the only C2 feedstock.Accordingly, in one embodiment of the present invention there isprovided an integrated process in which acetic acid is directlyconverted to ethylene in a single reaction zone with the ethylenefurther reacted with additional acetic acid in another reaction zone toform VAM. In another embodiment of the present invention there is alsoprovided an integrated process including hydrogenating acetic acidutilizing a first catalyst composition in a first reaction zone anddehydrating or cracking hydrogenated intermediates with a secondcatalyst in a second reaction zone to form ethylene with highselectivity, then reacting the ethylene in third reaction zone withacetic acid to produce VAM.

DETAILED DESCRIPTION OF INVENTION

The invention is described in detail below with reference to numerousembodiments for purposes of exemplification and illustration only.Modifications to particular embodiments within the spirit and scope ofthe present invention, set forth in the appended claims, will be readilyapparent to those of skill in the art.

Unless more specifically defined below, terminology as used herein isgiven its ordinary meaning. % and like terms refer to mole percentunless otherwise indicated.

“Conversion” is expressed as a mole percentage based on acetic acid inthe feed. The conversion of acetic acid (AcOH) is calculated from gaschromatography (GC) data using the following equation:

${{AcOH}\mspace{14mu}{conversion}\mspace{14mu}(\%)} = {100*\frac{\begin{matrix}{{{mmol}\mspace{14mu}{AcOH}\mspace{14mu}{in}\mspace{14mu}\left( {{feed}\mspace{14mu}{stream}} \right)} -} \\{{mmol}\mspace{14mu}{AcOH}\mspace{14mu}{out}\mspace{14mu}({GC})}\end{matrix}}{{mmol}\mspace{14mu}{AcOH}\mspace{14mu}{in}\mspace{14mu}\left( {{feed}\mspace{14mu}{Stream}} \right)}}$

“Selectivity” is expressed as a mole percent based on converted aceticacid. For example, if the conversion is 50 mole % and 50 mole % of theconverted acetic acid is converted to ethylene, we refer to the ethyleneselectivity as 50%. Selectivity is calculated from gas chromatography(GC) data as follows:

${{Ethylene}\mspace{14mu}{Selectivity}},\mspace{14mu}{\% = {100*\frac{{mmol}\mspace{14mu}{Ethylene}\mspace{14mu}{{out}({GC})}}{\frac{{Total}\mspace{14mu}{mmol}\mspace{14mu}{{Cout}({GC})}}{2} - {{mmol}\mspace{14mu}{AcOH}\mspace{14mu}{out}\mspace{14mu}({GC})}}}}$Stage 1. Formation of Ethylene from Acetic Acid

For purposes of convenience, we refer herein to the formation ofethylene from acetic acid as “stage 1” of the inventive process whetherthis aspect of the process takes place in one reaction zone or a seriesof reaction zones as described herein.

Without intending to be bound by theory, it is believed the conversionof acetic acid to ethylene in accordance with the stage 1 of the processof this invention proceeds in accordance with one or more of thefollowing chemical equations:

Step 1a: Hydrogenation of Acetic Acid to Ethylene.

Step 1b: Hydrogenation of Acetic Acid to Ethanol.

Step 1c: Hydrogenation of Acetic Acid to Ethyl Acetate.

Step 2a: Cracking of Ethyl Acetate to Ethylene and Acetic Acid.

Step 2b: Dehydration of Ethanol to Ethylene.

Step c: Oxidative Addition of Acetic Acid to Ethylene to form VAM

In accordance with one embodiment of the present invention regardingmaking ethylene for further conversion to VAM, conversion of acetic acidto ethylene is carried out in a single reaction zone which may be asingle fixed bed, for example. The fixed bed can comprise a mixture ofdifferent catalyst particles or catalyst particles which includemultiple catalysts. Typically, at least a hydrogenating catalyst isincluded in the reaction zone and optionally there is included adehydrating and/or cracking catalyst as well.

Various hydrogenating catalysts known to one skilled in the art can beemployed in hydrogenating acetic acid to ethanol in the first step ofthe process of this invention. The hydrogenating catalysts that aresuitable are the ones which are metal catalysts on a suitable support.As noted earlier, the following catalysts may be mentioned without anylimitation: copper, cobalt, ruthenium, nickel, aluminum, chromium, zinc,palladium and a mixture thereof. Typically, a single metal, a bimetalliccatalyst or a trimetallic catalyst on a suitable support can be used asa hydrogenating catalyst. Thus either copper alone or in combinationwith aluminum, chromium or zinc are particularly preferred. Similarly,cobalt alone or in combination with ruthenium is preferred. Examples ofadditional metals that can be used with cobalt as a second or thirdmetal include without any limitation the following: platinum, palladium,rhodium, rhenium, iridium, chromium, copper, tin, molybdenum, tungstenand vanadium.

Various catalyst supports known in the art can be used to support thecatalysts of this invention. Examples of such supports include withoutany limitation, zeolite, iron oxide, silica, alumina, titania, zirconia,magnesium oxide, calcium silicate, carbon, graphite and a mixturethereof. Preferred supports are H-ZSM-5, iron oxide, silica, calciumsilicate, carbon or graphite. It is also important to note that thehigher the purity of silica the better it is preferred as a support inthis invention.

Specific examples of supported hydrogenating catalysts include zeolite,such as H-ZSM-5, iron oxide, silica, alumina, titania, zirconia,magnesium oxide, calcium silicate, carbon, graphite and a mixturethereof. Particularly, as noted above, copper supported on iron oxide,copper-aluminum catalyst, cobalt supported on H-ZSM-5, a bimetalliccatalyst ruthenium-cobalt supported on silica, cobalt supported oncarbon are preferred.

A few of the commercially available catalysts include the following:copper-aluminum catalyst sold under the name of T-4489 by Sud Chemie;copper-zinc catalysts sold under the name of T-2130, T-4427 and T-4492;copper-chromium catalysts sold under the name of T-4419 and G-99B; andnickel catalysts sold under the name of NiSAT 310, C47-7-04, G-49, andG-69; all sold by Sud Chemie. Copper-aluminum catalyst sold under thename of T-4489 is particularly preferred.

The amount of metal loading on a support is not very critical in thisinvention and can vary in the range of about 3 weight percent to about10 weight percent. A metal loading of about 4 weight percent to about 6weight percent based on the weight of the support is particularlypreferred. Thus for example, 4 to 6 weight percent of copper supportedon iron oxide is particularly a preferred catalyst.

The metal impregnation can be carried out using any of the known methodsin the art. Typically, before impregnation the supports are dried at120° C. and shaped to particles having size distribution in the range ofabout 0.2 to 0.4 mm Optionally the supports may be pressed, crushed andsieved to a desired size distribution. Any of the known methods to shapethe support materials into desired size distribution can be employed.

For supports having low surface area, such as for example alpha-aluminaor iron oxide, the metal solutions are added in excess until completewetness or excess liquid impregnation so as to obtain desirable metalloadings.

As noted above, a few of the hydrogenating catalysts are bimetallic.Generally, in such cases, one metal acts as a promoter metal and theother metal is the main metal. For instance copper, nickel, cobalt andiron are considered to be main metals for preparing hydrogenatingcatalysts of this invention. The main metal can be combined with apromoter metal such as tungsten, vanadium, molybdenum, chromium or zinc.However, it should be noted that sometimes main metal can also act as apromoter metal or vice versa. For example, nickel can be used as apromoter metal when iron is used as a main metal. Similarly, chromiumcan be used as a main metal in conjunction with copper (i.e., Cu—Cr asmain bimetallic metals), which can further be combined with promotermetals such as cerium, magnesium or zinc.

The bimetallic catalysts are generally impregnated in two steps. First,the “promoter” metal is added, followed by “main” metal. Eachimpregnation step is followed by drying and calcination. The bimetalliccatalysts may also be prepared by co-impregnation. In the case oftrimetallic Cu/Cr-containing catalysts as described above, a sequentialimpregnation may be used, starting with the addition of the “promoter”metal. The second impregnation step may involve co-impregnation of thetwo principal metals, i.e., Cu and Cr. For example, Cu—Cr—Ce on SiO₂ maybe prepared by a first impregnation of cerium nitrate, followed by theco-impregnation of copper and chromium nitrates. Again, eachimpregnation is followed by drying and calcinations. In most cases, theimpregnation may be carried out using metal nitrate solutions. However,various other soluble salts which upon calcination releases metal ionscan also be used. Examples of other suitable metal salts forimpregnation include metal hydroxide, metal oxide, metal acetate,ammonium metal oxide, such as ammonium heptamolybdate hexahydrate, metalacids, such as perrhenic acid solution, metal oxalate, and the like.

As already noted above, any of the known zeolites can be used as supportcatalysts. A wide variety of zeolite catalysts are known in the artincluding synthetic as well as natural, all of which can be used assupport catalysts in this invention. More particularly, any zeolitehaving a pore diameter of at least about 0.6 nm can be used, preferablyemployed among such zeolites are the catalysts selected from the groupconsisting of mordenites, ZSM-5, a zeolite X and a zeolite Y.

The preparation of large-pore mordenites is described, for example, inU.S. Pat. No. 4,018,514 to Plummer and in Mol. Sieves. Pap. Conf., 1967,78, Soc. Chem. Ind. London, by D. DOMINE and J. QUOBEX.

Zeolite X is described, for example, U.S. Pat. No. 2,882,244 to Miltonand zeolite Y in U.S. Pat. No. 3,130,007 to Breck.

Various zeolites and zeolite-type materials are known in the art for thecatalysis of chemical reactions. For example, U.S. Pat. No. 3,702,886,to Argauer, discloses a class of synthetic zeolites, characterized as“Zeolite ZSM-5”, which are effective for the catalysis of varioushydrocarbon conversion processes.

The zeolites suitable for the procedure of the invention can be in thebasic form, in the partially or totally acidified form, or in thepartially dealuminated form.

In another aspect, any known dehydration catalysts can be employed inthe reaction zone of the process of this invention. Typically, a zeolitecatalyst is employed as a dehydration catalyst and may support adehydrogenating catalyst. While any zeolite having a pore diameter of atleast about 0.6 nm can be used, preferably employed among such zeolitesare the dehydration catalyst selected from the group consisting ofmordenites, ZSM-5, a zeolite X and a zeolite Y.

An active dehydrating catalyst, characterized as “H-ZSM-5” or“H-mordenite” zeolites are prepared from a corresponding “ZSM-5” zeoliteor “mordenite” zeolite by replacing most, and generally at least about80% of the cations of the latter zeolite with hydrogen ions usingtechniques well-known in the art. H-mordenite zeolite, for example, wasprepared by calcination of ammonium form mordenite at 500-550° C. for4-8 hours. If the sodium form of mordenite is used as a precursor, thesodium mordenite is ion-exchanged to ammonium form prior to calcination.

These zeolite catalysts are essentially crystalline aluminosilicates orin the neutral form a combination of silica and alumina in a welldefined crystalline structure. In a particularly preferred class ofzeolite catalysts for purposes of the present invention, the molar ratioof SiO₂ to Al₂O₃ in these zeolites is within the ratio of about 10 to60.

As noted earlier, ethylene is produced by dehydration as well as thedecomposition or “cracking” of ethyl acetate to ethylene and aceticacid. This may simply occur as thermal cracking at elevated temperaturesor may be a catalyzed reaction if so desired, utilizing a crackingcatalyst. Suitable cracking catalysts include sulfonic acid resins suchas perfluorosulfonic acid resins disclosed in U.S. Pat. No. 4,399,305 toSchreck noted above, the disclosure of which is incorporated byreference. Zeolites are also suitable as cracking catalysts as noted inU.S. Pat. No. 4,620,050 to Cognion et al., the disclosure of which isalso incorporated by reference. Thus, a zeolite catalyst may be used toconcurrently dehydrate ethanol to ethylene and decompose ethyl acetateto ethylene in a highly efficient process of the invention.

Selectivities of acetic acid to ethylene are suitably more than 10% andmore such as at least 20%, at or least 25% or so up to about 40% intypical cases. Depending on the by-product mix, it may be desirable tooperate at intermediate selectivities, and recirculate products such asacetaldehyde for further hydrogenating and dehydration providedselectivity to undesirable products such as CO₂ remains low.

Preferably, for the purposes of the process of this invention, thesuitable hydrogenating catalyst is either copper on iron oxide orcopper-aluminum catalyst, sold under the tradename of T-4489 by SudChemie, cobalt supported on H-ZSM-5, a bimetallic catalyst, rutheniumand cobalt supported on silica, and cobalt supported on carbon. In thisembodiment of the process of this invention, the copper loading on theiron oxide support or in the bimetallic copper-aluminum catalyst istypically in the range of about 3 weight percent to about 10 weightpercent, preferably it is in the range of about 4 weight percent toabout 6 weight percent. Similarly, the loading of cobalt on H-ZSM-5 orsilica or carbon is typically around 5 weight percent. The amount ofruthenium in the bimetallic catalyst is also around 5 weight percent.

In addition, the acetic acid hydrogenation and dehydration are carriedout at a pressure just sufficient to overcome the pressure drop acrossthe catalytic bed.

The reaction may be carried out in the vapor or liquid state under awide variety of conditions. Preferably, the reaction is carried out inthe vapor phase. Reaction temperatures may be employed, for example inthe range of about 200° C. to about 375° C., preferably about 250° C. toabout 350° C. The pressure is generally uncritical to the reaction andsubatmospheric, atmospheric or superatmospheric pressures may beemployed. In most cases, however, the pressure of the reaction will bein the range of about 1 to 30 atmospheres absolute.

Although the reaction consumes two moles of hydrogen per mole of aceticacid to produce a mole of ethylene, the actual molar ratio of aceticacid to hydrogen in the feed stream may be varied between wide limits,e.g. from about 100:1 to 1:100. It is preferred however that such ratiobe in the range of about 1:20 to 1:2.

It is well known to produce acetic acid through methanol carbonylation,acetaldehyde oxidation, ethylene oxidation, oxidative fermentation, andanaerobic fermentation and so forth. As petroleum and natural gas havebecome more expensive, methods for producing acetic acid andintermediates such as methanol and carbon monoxide from alternate carbonsources have drawn more interest.

Of particular interest is the production of acetic acid from synthesisgas (syngas) that may be derived from any suitable carbon source. U.S.Pat. No. 6,232,352 to Vidalin, the disclosure of which is incorporatedherein by reference, for example, teaches a method of retrofitting amethanol plant for the manufacture of acetic acid. By retrofitting amethanol plant the large capital costs associated with CO generation fora new acetic acid plant are significantly reduced or largely eliminated.All or part of the syngas is diverted from the methanol synthesis loopand supplied to a separator unit to recover CO and hydrogen, which arethen used to produce acetic acid. In addition to acetic acid, theprocess can also be used to make hydrogen which is utilized inconnection with this invention.

U.S. Pat. No. RE 35,377 to Steinberg et al., also incorporated herein byreference, provides a method for the production of methanol byconversion of carbonaceous materials such as oil, coal, natural gas andbiomass materials. The process includes hydrogasification of solidand/or liquid carbonaceous materials to obtain a process gas which issteam pyrolized with additional natural gas to form synthesis gas. Thesyngas is converted to methanol which may be carbonylated to aceticacid. The method likewise produces hydrogen which may be used inconnection with this invention as noted above. See also, U.S. Pat. No.5,821,111 to Grady et al., which discloses a process for convertingwaste biomass through gasification into synthesis gas as well as U.S.Pat. No. 6,685,754 to Kindig et al., the disclosures of which areincorporated herein by reference.

The acetic acid may be vaporized at the reaction temperature, and thenit can be fed along with hydrogen in an undiluted state or diluted statewith a relatively inert carrier gas, such as nitrogen, argon, helium,carbon dioxide and the like.

Alternatively, acetic acid in vapor form may be taken directly as crudeproduct from the flash vessel of a methanol carbonylation unit of theclass described in U.S. Pat. No. 6,657,078 to Scates et al., thedisclosure of which is incorporated by reference. The crude vaporproduct may be fed directly to the reaction zones of the presentinvention without the need for condensing the acetic acid and light endsor removing water, saving overall processing costs.

Contact or residence time can also vary widely, depending upon suchvariables as the amount of acetic acid, catalyst, reactor, temperatureand pressure. Typical contact times range from a fraction of a second tomore than several hours when a catalyst system other than a fixed bed isused, with preferred contact times, at least for vapor phase reactions,between about 0.5 and 100 seconds.

Typically, the catalyst is employed in a fixed bed reactor e.g. in theshape of an elongated pipe or tube where the reactants, typically in thevapor form, are passed over or through the catalyst. Other reactors,such as fluid or ebullient bed reactors, can be employed, if desired. Insome instances, it is advantageous to use the catalyst bed inconjunction with an inert material such as glass wool to regulate thepressure drop of the reactant stream through the catalyst bed and thecontact time of the reactant compounds with the catalyst particles.

In one of the examples there is provided a process for selectiveformation of ethylene from acetic acid comprising: contacting a feedstream of acetic acid and hydrogen at a temperature in the range ofabout 250° C. to 350° C. with a catalyst chosen from copper supported oniron oxide, copper-aluminum catalyst, cobalt supported on H-ZSM-5,ruthenium-cobalt supported on silica or cobalt supported on carbon toform ethylene.

In one of the examples, the preferred catalyst is 5 weight percentcopper on iron oxide, 5 weight percent cobalt on H-ZSM-5, 5 weightpercent cobalt and 5 weight percent ruthenium on silica or 5 weightpercent cobalt on carbon. In this embodiment of the process of thisinvention it is preferred that the reaction is carried out in the vaporphase in a tubular reactor packed with the catalyst bed and at atemperature in the range of about 250° C. to 350° C. and at a pressurein the range of about 1 to 30 atmospheres absolute, and the contact timeof reactants is in the range of about 0.5 and 100 seconds.

Stage 2. Formation of VAM from the Gaseous Product Stream ContainingEthylene and Additional Amounts of Acetic Acid

As noted earlier, for purposes of convenience we refer to the reactionof the ethylene formed in stage 1 with additional acetic acid and oxygento form VAM as “stage 2” of the inventive process herein, whether or notmore than 2 specific process steps are involved in the conversion.

In a second (or third depending upon the process parameters used for theformation of product stream containing ethylene) reactor zone thegaseous product stream from the hydrogenating reactor is contactedfurther with a catalyst and a second feed containing molecular oxygenand additional amounts of acetic acid. It is preferable that equal moleratios of ethylene and acetic acid are fed into this reactor zone.

Any of the known catalysts for oxidative reaction of ethylene withacetic acid to form VAM can be employed in stage 2 of the process ofthis invention, for example, as described in GB 1 559 540, U.S. Pat.Nos. 5,185,308; 5,691,267; 6,114,571; and WO 99/08791 the equivalent toU.S. Pat. No. 6,603,038. EP-A 0 330 853 describes impregnated catalystsfor the production of VAM containing palladium, potassium, manganese andcadmium as additional promoter instead of gold. See also, U.S. Pat. No.6,852,877. All of the references mentioned immediately above areincorporated herein by reference in their entirety as relating toforming VAM from ethylene, acetic acid and oxygen.

GB 1 559 540 describes suitable catalysts that can be employed in thepreparation of VAM by the reaction of ethylene, acetic acid and oxygen,as used in step (d) of the process of this invention. The catalyst iscomprised of: (1) a catalyst support having a particle diameter of from3 to 7 mm and a pore volume of from about 0.2 to 1.5 ml/g, a 10% byweight water suspension of the catalyst support having a pH from about3.0 to 9.0, (2) a palladium-gold alloy distributed in a surface layer ofthe catalyst support, the surface layer extending less than 0.5 mm fromthe surface of the support, the palladium in the alloy being present inan amount of from about 1.5 to 5.0 grams per liter of catalyst, and thegold being present in an amount of from about 0.5 to 2.25 grams perliter of catalyst, and (3) from 5 to 60 grams per liter of catalyst ofalkali metal acetate.

U.S. Pat. No. 5,185,308 to Bartley et al. describes a shell impregnatedcatalyst active for the production of VAM from ethylene, acetic acid andan oxygen containing gas, the catalyst consisting essentially of (1) acatalyst support having a particle diameter from about 3 to about 7 mmand a pore volume of 0.2 to 1.5 ml per gram, (2) palladium and golddistributed in the outermost 1.0 mm thick layer of the catalyst supportparticles, and (3) from about 3.5 to about 9.5% by weight of potassiumacetate wherein the gold to palladium weight ratio in said catalyst isin the range 0.6 to 1.25.

U.S. Pat. No. 5,691,267 to Nicolau et al. describes a two step goldaddition method for a catalyst used in the gas phase formation of VAMfrom the reaction of ethylene, oxygen, and acetic acid. The catalyst isformed by (1) impregnating a catalyst carrier with aqueous solutions ofa water-soluble palladium salt and a first amount of a water-solublegold compound such as sodium-palladium chloride and auric chloride, (2)fixing the precious metals on the carrier by precipitating thewater-insoluble palladium and gold compounds by treatment of theimpregnated carriers with a reactive basic solution such as aqueoussodium hydroxide which reacts with the palladium and gold compounds toform hydroxides of palladium and gold on the carrier surface, (3)washing with water to remove the chloride ion (or other anion), and (4)reducing all the precious metal hydroxides to free palladium and gold,wherein the improvement comprises (5) impregnating the carrier with asecond amount of a water-soluble gold compound subsequent to fixing afirst amount of water-soluble gold agent, and (6) fixing the secondamount of a water-soluble gold compound.

U.S. Pat. No. 6,114,571 to Abel et al. describes a catalyst for formingvinyl acetate in the gas phase from ethylene, acetic acid, and oxygen oroxygen-containing gases wherein the catalyst is comprised of palladium,gold, boron, and alkali metal compounds on a support. The catalyst isprepared by a) impregnating the support with soluble palladium and goldcompounds; b) converting the soluble palladium and gold compounds on thesupport into insoluble compounds by means of an alkaline solution; c)reducing the insoluble palladium and gold compounds on the support bymeans of a reducing agent in the liquid phase; d) washing andsubsequently drying the support; e) impregnating the support with asoluble alkali metal compound; and f) finally drying the support at amaximum of 1500 C., wherein boron or boron compounds are applied to thecatalyst prior to the final drying.

WO 99/08791, the equivalent to U.S. Pat. No. 6,603,038 to Hagemeyer etal., describes a method for producing catalysts containing metalnanoparticles on a porous support, especially for gas phase oxidation ofethylene and acetic acid to form VAM. The invention relates to a methodfor producing a catalyst containing one or several metals from the groupof metals comprising the sub-groups Ib and VIIIb of the periodic tableon porous support particles, characterized by a first step in which oneor several precursors from the group of compounds of metals fromsub-groups Ib and VIIIb of the periodic table is or are applied to aporous support, and a second step in which the porous, preferablynanoporous support to which at least one precursor has been applied istreated with at least one reduction agent, to obtain the metalnanoparticles produced in situ in the pores of said support.

Typically, VAM formation of the process of the present invention iscarried out heterogeneously with the reactants being present in the gasphase.

The molecular oxygen-containing gas used in formation of VAM in theprocess of the present invention may comprise other inert gases such asnitrogen. Preferably molecular oxygen used in forming VAM is air.

Stage 2 of the process of the present invention may suitably be carriedout at a temperature in the range of from about 140° C. to 220° C. Stage2 of the process of the present invention may suitably be carried out ata pressure in the range of from about 1 to 100 atmospheres absolute.Stage 2 of the process of the present invention can be carried out inany suitable reactor design capable of removing the heat of reaction inan appropriate way; preferred technical solutions are fixed or fluidizedbed reactors as described herein.

Acetic acid conversions in the range of about 5 to 50% may be achievedin stage 2 of the process of the present invention. Oxygen conversionsin the range of about 20 to 100% may be achieved in stage 2 of thepresent invention. In stage 2 of the process of the present invention,the catalyst suitably has a productivity (space time yield, STY) in therange of about 100 to 2000 grams of vinyl acetate per hour per liter ofcatalyst, but >10000 grams of vinyl acetate per hour per liter ofcatalyst is also suitable.

As already noted above, the gaseous product stream from stage 2 of theprocess comprises VAM and water and optionally also unreacted aceticacid, ethylene, ethyl acetate, ethane, nitrogen, carbon monoxide, carbondioxide and possibly traces of other byproducts. Intermediate betweenstage 2 and VAM separation step of the process of the invention it ispreferred to remove ethylene, and ethane, carbon monoxide and carbondioxide, if any, from the product stream, suitably as an overheadgaseous fraction from a scrubbing column, in which a liquid fractioncomprising vinyl acetate, water and acetic acid is removed from thebase.

The product stream from stage 2 comprising VAM, water and acetic acid,with or without the intermediate scrubbing step, is separated in thefinal step by distillation into an overhead azeotrope fractioncomprising vinyl acetate and water and a base fraction comprising aceticacid.

VAM is recovered from the azeotrope fraction separated in stage 2process step of the invention, suitably for example by decantation. Therecovered VAM may, if desired, be further purified in known manner. Thebase fraction comprising acetic acid separated in stage 2 is preferablyrecycled, with or preferably without further purification, to stage 1or, if desired, to stage 2 of the process.

The following examples describe the procedures used for the preparationof various catalysts employed in the process of this invention.

EXAMPLE A Preparation of 5 Weight Percent Copper on Iron Oxide

Powdered and meshed iron oxide (95 g) of uniform particle sizedistribution of about 0.2 mm was dried at 120° C. in an oven undernitrogen atmosphere overnight and then cooled to room temperature. Tothis was added a solution of copper nitrate (17 g) in distilled water(100 ml). The resulting slurry was dried in an oven gradually heated to110° C. (>2 hours, 10° C./min) The impregnated catalyst mixture was thencalcined at 500° C. (6 hours, 1° C./min)

EXAMPLE B Preparation of H-Mordenite Zeolite

H-Mordenite zeolite was prepared by calcination of ammonium formMordenite at 500-550° C. for 4-8 hours. If the sodium form of Mordeniteis used as a precursor, the sodium Mordenite is ion-exchanged toammonium form prior to calcination.

EXAMPLE C Preparation of 5 Weight Percent Cobalt on H-ZSM-5

Example A is substantially repeated with the exception of usingappropriate amount of cobalt nitrate hexahydrate as the metal salt andH-ZSM-5 as the support catalyst to prepare 5 weight percent cobaltsupported on H-ZSM-5.

EXAMPLE D Preparation of 5 Weight Percent Cobalt and 5 Weight PercentRuthenium on Silica

Example A is substantially repeated with the exception of usingappropriate amounts of cobalt nitrate hexahydrate and ruthenium nitrosylnitrate as the metal salts and silica as the support catalyst to prepare5 weight percent cobalt and 5 weight percent ruthenium supported onsilica.

EXAMPLE E Preparation of 5 Weight Percent Cobalt on Carbon

Example A is substantially repeated with the exception of usingappropriate amount of cobalt nitrate hexahydrate as the metal salt andcarbon as the support catalyst to prepare 5 weight percent cobaltsupported on carbon.

EXAMPLE F

K, Pd, Au/TiO₂ catalyst for converting ethylene, acetic acid and oxygento VAM is prepared generally as follows:

2.11 g palladium acetate (Aldrich) and 1.32 g gold acetate is dissolvedin 30 ml acetic acid. The preparation of the employed gold acetate isdescribed e.g., in U.S. Pat. No. 4,933,204 to Warren, Jr. et al. 100 mlTiO₂ support (P25 pellets, Degussa, Hanau) are added to the palladiumand gold acetate solution. Then, the majority of acetic acid isevaporated using a rotary evaporator at 70° C., followed by evaporatingthe rest using an oil pump at 60° C. and finally in a vacuum dryingcabinet at 60° C. for 14 h.

The resulting pellets are reduced with a gas mixture of 10 vol %hydrogen in nitrogen, while passing the gas (40 l/h) directly throughthe pellets at 500° C. and 1 bar for 1 h. For loading with potassiumions, the reduced pellets are added to a solution containing 4 gpotassium acetate in 30 ml of water, for 15 minutes in a mixingapparatus.

Then, the solvent is evaporated using a rotary evaporator. The pelletsare dried at 100° C. for 14 h.

EXAMPLE G Preparation of Pd and Au

A vinyl acetate catalyst containing Pd and Au for converting a stream ofgas containing ethylene, oxygen or air, and acetic acid into VAM isprepared generally as follows:

the catalyst is prepared on spherical silica supports with diameters ofabout 5 mm (SudChemie). The silica supports are impregnated with anaqueous solution containing sodium palladium tetrachlorate and sodiumtetracholroaurate in sufficient amounts such that the catalysts wouldhave about 7 gm/l of palladium metal and about 7 gm/l of gold metaleach.

After impregnation, the carrier is placed in a roto-evaporator, withoutvacuum, and treated with 283 ml of a 50% w/w aqueous solution of sodiumhydroxide. The supports are rotated at about 5 rpm for about 2.5 hoursin a sodium hydroxide solution at a temperature of 70° C. by rotation ina hot water bath. The resulting catalysts are reduced in a gas blend of5% ethylene in nitrogen for about 5 hours at a temperature of about 150°C. at a flow rate of about 0.5 SCFH (standard cubic feet per hour) atatmospheric pressure to reduce the metal salts to metal.

The catalysts are then impregnated again with an aqueous solution ofsodium tetrachloroaurate and 1.65 gm of a 50% w/w aqueous sodiumhydroxide fixing solution. The resulting catalysts are reduced in a gasblend of 5% ethylene in nitrogen for about 5 hours at a temperature ofabout 150° C. at a flow rate of about 0.5 SCFH (standard cubic feet perhour) at atmospheric pressure to reduce the gold salts to gold metal.

EXAMPLE H Preparation of Pd, Au, and K

A catalyst for preparing vinyl acetate in the gas phase from ethylene,acetic acid, and oxygen or oxygen-containing gases wherein the catalystis prepared generally as follows:

250 ml of silicon dioxide catalyst sphere supports having a diameter of7.3 mm (Sud Chemie) were impregnated with 85 ml of an aqueous solutioncontaining 4.6 g of Na₂PdCl₄ and 1.4 g of NaAuCl₄. The precipitation ofthe insoluble metal compounds is achieved by the addition of 283 ml ofan aqueous solution of 17 g of borax. The vessel is then immediatelyrotated by means of a rotary evaporator, without vacuum, for 2.5 hoursat 5 revolutions per minute (rpm). The reduction is achieved by theaddition of 7 ml of hydrazine hydrate in 20 ml of water and immediaterotation of the vessel at 5 rpm for 1 hour.

The pellets thus obtained were dried for 1 hour at 1000 C. The reducedcatalyst is impregnated with an aqueous solution containing 10 g ofpotassium acetate and having a volume corresponding to the absorptioncapacity of the dry support material. The catalyst is then dried again.

EXAMPLE I Preparation of Pd, Au, and B

A catalyst containing nanosize metal particles on a porous support forthe gas phase oxidation of ethylene and acetic acid to give vinylacetate is prepared as follows:

200 g of Si02 supports (Siliperl AF125, Engelhard) having a BET surfacearea of 300 m²/g were sprayed discontinuously at a temperature of 30-32°C. with a hydro-chloric acid solution of 3.33 g (18.8 mmol) of palladiumchloride and 1.85 g (4.7 mmol) of auric acid in 500 ml of water over aperiod of 35 minutes in a coating unit.

The support spheres were subsequently dried and sprayed with 20 g oftripotassium citrate hydrate dissolved in 200 ml of water over a periodof 25 minutes. At a drum rotation speed of 10 rpm, spraying is carriedout discontinuously at 1 bar. The inlet temperature (warm airtemperature) is 60° C. and the product temperature is 32-30° C. Thisgave a homogeneously impregnated coated catalyst having a shellthickness of 400 μm. The diameter of the nanosize particles isdetermined by means of TEM. The mean particle diameter is 30 nm.

Gas Chromatographic (GC) analysis of the Products

The analysis of the products is carried out by online GC. A threechannel compact GC equipped with one flame ionization detector (FID) and2 thermal conducting detectors (TCDs) is used to analyze the reactantsand products. The front channel was equipped with an FID and a CP-Sil 5(20 m)+WaxFFap (5 m) column and was used to quantify:

-   -   Acetaldehyde    -   Ethanol    -   Acetone    -   Methyl acetate    -   Vinyl acetate    -   Ethyl acetate    -   Acetic acid    -   Ethylene glycol diacetate    -   Ethylene glycol    -   Ethylidene diacetate    -   Paraldehyde

The middle channel was equipped with a TCD and Porabond Q column and wasused to quantify:

-   -   CO₂    -   Ethylene    -   Ethane

The back channel was equipped with a TCD and Molsieve 5A column and wasused to quantify:

-   -   Helium    -   Hydrogen    -   Nitrogen    -   Methane    -   Carbon monoxide

Prior to reactions, the retention time of the different components wasdetermined by spiking with individual compounds and the GCs werecalibrated either with a calibration gas of known composition or withliquid solutions of known compositions. This allowed the determinationof the response factors for the various components.

Examples 1 and 2 illustrate the formation of ethylene in a dual reactionzone using two catalysts, hydrogenation and dehydration catalysts, inthe stage 1 of the process of this invention.

EXAMPLE 1

The catalysts utilized were a copper on iron oxide catalyst, T-4489purchased from Sud Chemie and an H-mordenite zeolite prepared byreplacing with hydrogen ions all but 500 ppm based on the weight of thezeolite of the sodium ions in a sodium aluminosilicate mordenitecatalyst prepared in accordance with U.S. Pat. No. 4,018,514 to Plummeror equivalent in which the ratio of silica to alumina is preferably inthe range of from about 15:1 to about 100:1. A suitable catalyst isCBV21A available from Zeolyst International, which has a silica toalumina ratio of about 20:1.

In a tubular reactor made of stainless steel, having an internaldiameter of 30 mm and capable of being raised to a controlledtemperature, there are arranged 30 ml of 5 weight percent copper on ironoxide catalyst as top layer and 20 ml of H-mordenite as a bottom layer.The length of the combined catalyst bed after charging was approximatelyabout 70 mm.

A feed liquid was composed essentially of acetic acid. The reaction feedliquid was evaporated and charged to the reactor along with hydrogen andhelium as a carrier gas with an average combined gas hourly spacevelocity (GHSV) of 2500 hr⁻¹ at a temperature of 300° C. and pressure of100 psig. The feed stream contained a mole percent of acetic acid fromabout 6.1% to about 7.3% and mole percent of hydrogen from about 54.3%to about 61.5%. The feed stream was supplied to the hydrogenationcatalyst (top) layer first such that the stream with hydrogenated aceticacid intermediates then contacted the dehydration catalyst layer. Aportion of the vapor effluent from the reactor was passed through a gaschromatograph for analysis of the contents of the effluents. The aceticacid conversion was 65% and ethylene selectivity was 85%. Selectivity toacetone was 3%, selectivity to ethyl acetate was 2% and selectivity toethanol was 0.6%. Carbon dioxide was relatively low; the measuredselectivity to CO₂ of the acetic acid converted was 4%.

EXAMPLE 2

The catalysts utilized were 5 weight percent copper on iron oxideprepared in accordance with the procedure of Example A and anH-mordenite zeolite prepared by replacing with hydrogen ions all but 500ppm based on the weight of the zeolite of the sodium ions in a sodiumaluminosilicate mordenite catalyst as noted above in Example 1.

The procedure as set forth in Example 1 was substantially repeated withan average combined gas hourly space velocity (GHSV) of 2500 hr⁻¹ of thefeed stream of vaporized acetic acid, hydrogen and helium at atemperature of 350° C. and pressure of 100 psig. The resulting feedstream contained a mole percent of acetic acid of about 7.3% and molepercent of hydrogen of about 54.3%. A portion of the vapor effluent waspassed through a gas chromatograph for analysis of the contents of theeffluents. The acetic acid conversion was 8% and ethylene selectivitywas 18%.

Generally speaking, selectivities to ethylene above 10% or so are highlydesirable; it being appreciated that the other by-products such asethanol or ethyl acetate can be re-cycled to the reactor along withunreacted acetic acid, while still other by-products can be re-processedor used for fuel value. Selectivities to CO₂ of less than 10% aredesired, preferably less than 5%.

COMPARATIVE EXAMPLES 1A-5A

These examples illustrate the reaction of acetic acid and hydrogen overa variety of catalysts wherein either no ethylene was formed and/or verylow levels of ethylene was detected.

In all of these examples the procedure as set forth in Example 1 wassubstantially followed with the exception of using different catalystsas listed in Table 1. As summarized in Table 1, in all of thesecomparative examples only one single layer of catalyst was used. Thereaction temperature and selectivity to ethylene are also tabulated inTable 1.

TABLE 1 Reactor Mol % Mol % Acetic Reactor Temperature H₂ in Feed Acidin Ethylene Bed Catalyst (° C.) Stream Feed Stream Selectivity Single0.5%-1% 250-350° C. 54.2% 7.3% 0% Layer Pd on Carbon Single 1% Ru on250-350° C. 36.8% 7.3% 0% Layer Carbon Single 2% Pt on 350° C.34.3%-76.5% 4.4%-7.3% 0%-1%  Layer Fe₂O₃ Single 2.58% Pd/ 250-350° C.36.8% 7.3% 0%-0.5% Layer 5.05% Mo on SiO₂ Single 4.79% Cu 400° C. 35.2%7.5%  0%-2.25% Layer on SiO2

In these examples various other products including acetaldehyde,ethanol, ethyl acetate, ethane, carbon monoxide, carbon dioxide,methane, isopropanol, acetone and water were detected.

Examples 3-6 illustrate formation of ethylene in a single reactor in theStage 1 of the process of this invention.

EXAMPLE 3

The catalyst utilized was 5 weight percent copper on iron oxide preparedin accordance with the procedure of Example A.

In a tubular reactor made of stainless steel, having an internaldiameter of 30 mm and capable of being raised to a controlledtemperature, there are arranged 50 ml of 5 weight percent copper on ironoxide catalyst. The length of the catalyst bed after charging wasapproximately about 70 mm.

A feed liquid was composed essentially of acetic acid. The reaction feedliquid was evaporated and charged to the reactor along with hydrogen andhelium as a carrier gas with an average combined gas hourly spacevelocity (GHSV) of about 2500 hr⁻¹ at a temperature of about 350° C. andpressure of 100 psig. The resulting feed stream contained a mole percentof acetic acid from about 4.4% to about 13.8% and the mole percent ofhydrogen from about 14% to about 77%. A portion of the vapor effluentwas passed through a gas chromatograph for analysis of the contents ofthe effluents. Results appear in Table 2. The selectivity to ethylenewas 16% at an acetic acid conversion of 100%

EXAMPLE 4

The catalyst utilized was 5 weight percent cobalt on H-ZSM-5 prepared inaccordance with the procedure of Example C.

The procedure as set forth in Example 3 was substantially repeated withan average combined gas hourly space velocity (GHSV) of 10,000 hr⁻¹ ofthe feed stream of the vaporized acetic acid, hydrogen and helium at atemperature of 250° C. and pressure of 1 bar. A portion of the vaporeffluent was passed through a gas chromatograph for analysis of thecontents of the effluents. Results appear in Table 2. The acetic acidconversion was 3% and ethylene selectivity was 28%.

EXAMPLE 5

The catalyst utilized was a bimetallic catalyst containing 5 weightpercent cobalt and 5 weight percent ruthenium supported on silicaprepared in accordance with the procedure of Example D.

The procedure as set forth in Example 1 was substantially repeated withan average combined gas hourly space velocity (GHSV) of 2500 hr⁻¹ of thefeed stream of the vaporized acetic acid, hydrogen and helium at atemperature of 350° C. and pressure of 1 bar. A portion of the vaporeffluent was passed through a gas chromatograph for analysis of thecontents of the effluents. Results appear in Table 2. The acetic acidconversion was 4% and ethylene selectivity was 14%.

EXAMPLE 6

The catalyst utilized was 5 weight percent cobalt supported on carbonprepared in accordance with the procedure of Example E.

The procedure as set forth in Example 1 was substantially repeated withan average combined gas hourly space velocity (GHSV) of 2500 hr⁻¹ of thefeed stream of the vaporized acetic acid, hydrogen and helium at atemperature of 350° C. and pressure of 1 bar. A portion of the vaporeffluent was passed through a gas chromatograph for analysis of thecontents of the effluents. Results appear in Table 2. The acetic acidconversion was 2% and ethylene selectivity was 12%.

Generally speaking, selectivities to ethylene above 10% or so are highlydesirable; it being appreciated that the other by-products such asethanol or ethyl acetate can be re-cycled to the reactor along withunreacted acetic acid, while still other by-products can be re-processedor used for fuel value. Selectivities to CO₂ of less than 10% aredesired, preferably 5% or less.

TABLE 2 Acetic Acid Conversion and Selectivities Ethylene Acetic acidselectivity conversion Example (%) (%) Other products 3 16 100acetaldehyde-31%, ethane-15%, ethyl acetate-4%, CO₂-5% 4 29 3acetaldehyde-51%, ethane-28% 5 14 4 acetaldehyde-78%, ethane-8% 6 12 2acetone-8%, methane-47%, ethane-5%

COMPARATIVE EXAMPLES 6A-10A

These examples illustrate the reaction of acetic acid and hydrogen overa variety of catalysts wherein either no ethylene was formed and/or verylow levels of ethylene was detected.

In all of these examples the procedure as set forth in Example 3 wassubstantially followed with the exception of using different catalystsas listed in Table 3. The reaction temperature and selectivity toethylene are also tabulated in Table 3.

TABLE 3 Reactor Temperature Mol % Mol % Acetic Ethylene Catalyst (° C.)H₂ In Feed Acid In Feed Selectivity 0.5%-1% Pd on Carbon 250-350° C.54.2% 7.3% 0% 1% Ru on Carbon 250-350° C. 36.8% 7.3% 0% 2% Pt on Fe₂O₃350° C. 34.3%-76.5% 4.4%-7.3% 0%-1%  2.58% Pd/5.05% Mo 250-350° C. 36.8%7.3% 0%-0.5% on SiO₂ 4.79% Cu on SiO2 400° C. 35.2% 7.5%  0%-2.25%

In these examples various other products including acetaldehyde,ethanol, ethyl acetate, ethane, carbon monoxide, carbon dioxide,methane, isopropanol, acetone and water were detected.

EXAMPLE 7

The catalyst utilized to convert ethylene, acetic acid and oxygen to VAMis K, Pd, Au/TiO₂ prepared in accordance with the procedure of Example Fabove. The procedure as set forth in U.S. Pat. No. 6,852,877 to Zeyss etal. is used to carry out stage 2 of the process of the present inventionusing one of the feed streams from Examples 1-6, stage 1 of the processof the present invention and molecular oxygen in combination withstoichiometric amounts of acetic acid.

Typical reaction conditions and selectivities for stage 2 are as setforth in Table 4 below.

TABLE 4 Vinyl Acetate Synthesis Reaction Results Conditions SelectivitySpace Time Yield T [° C.] P [bar] S (VAM) [%] STY [g/(h)] 155 9 98 1000160 9 98 1050 170 9 96 1000 160 9 98 1350 170 9 97 700 170 9 98 1300

EXAMPLE 8

A catalyst utilized to convert ethylene, oxygen, and acetic acid to VAMis Pd/Au prepared in accordance with the procedure of Example G above.The procedure as set forth in U.S. Pat. No. 5,691,267 to Nicolau et al.is used to carry out stage 2 of the process of the present inventionusing one of the feed streams from Examples 1-6, stage 1 of the processof the present invention, and molecular oxygen in combination withstoichiometric amounts of acetic acid.

EXAMPLE 9

A catalyst utilized to convert ethylene, oxygen, and acetic acid to VAMis Pd/Au and boron prepared in accordance with the procedure of ExampleH above. The procedure as set forth in U.S. Pat. No. 6,114,571 to Abelet al. is used to carry out stage 2 of the process of the presentinvention using one of the feed streams from Examples 1-6, stage 1 ofthe process of the present invention, and molecular oxygen incombination with stoichiometric amounts of acetic acid.

EXAMPLE 10

A catalyst utilized to convert ethylene, oxygen, and acetic acid to VAMhas metal containing nanoparticles on a porous support prepared inaccordance with the procedure of Example I above. The procedure as setforth in U.S. Pat. No. 6,603,038 to Hagemeyer et al. is used to carryout stage 2 of the process of the present invention using one of thefeed streams from Examples 1-6, stage 1 of the process of the presentinvention.

While it is known to react acetic acid with ethylene in order to produceVAM. It has now been unexpectedly found that ethylene can be made on anindustrial scale directly from acetic acid with high selectivity andyield. As demonstrated from the Examples above, ethylene can beeconomically manufactured cost effectively in order to produce VAM andother products made from ethylene.

While the invention has been described in detail, modifications withinthe spirit and scope of the invention will be readily apparent to thoseof skill in the art. In view of the foregoing discussion, relevantknowledge in the art and references discussed above in connection withthe Background and Detailed Description, the disclosures of which areall incorporated herein by reference, further description is deemedunnecessary.

1. A process for the production of vinyl acetate from acetic acidcomprising: a. contacting in a first reaction zone acetic acid andhydrogen at an elevated temperature with a first catalyst compositioncontaining a metal selected from the group consisting of copper, nickel,aluminum, chromium, zinc, palladium and mixtures thereof on a support toform an intermediate hydrogenated mixture comprising ethanol and ethylacetate; b. reacting said intermediate hydrogenated mixture over asecond catalytic composition which includes a suitable dehydratingcatalyst comprising a zeolite catalyst selected from the groupconsisting of H-mordenite, ZSM-5, a zeolite X and a zeolite Y, andoptionally said second catalytic composition includes a crackingcatalyst, in a second reaction zone to form a first gaseous productstream containing ethylene; c. enriching said first gaseous productstream with ethylene at least up to 50 percent; d. contacting in a thirdreaction zone said enriched first gaseous product stream in combinationwith acetic acid and molecular oxygen in the presence of a thirdcatalyst to form a second gaseous product stream comprising vinylacetate; and e. separating the vinyl acetate from said second gaseousproduct stream.
 2. The process according to claim 1, wherein the supportof the first catalyst composition is selected from the group consistingof iron oxide, zeolites, silica, alumina, titania, zirconia, magnesia,calcium silicate, carbon, graphite and mixtures thereof.
 3. The processaccording to claim 1, wherein the first catalyst composition is selectedfrom the group consisting of copper supported on iron oxide,copper-aluminum catalyst, copper-zinc catalyst, copper-chromiumcatalyst, cobalt supported on H-ZSM-5, ruthenium-cobalt supported onsilica, cobalt supported on carbon, and nickel catalyst.
 4. The processaccording to claim 1, wherein the hydrogenation in step (a) is carriedout at a pressure just sufficient to overcome the pressure drop acrossthe first reaction zone.
 5. The process according to claim 1, whereinthe reactants in step (a) consist of acetic acid and hydrogen with amolar ratio in the range of about 100:1 to 1:100, the temperature is inthe range of about 250° C. to 350° C., and the pressure is in the rangeof about 1 to 30 atmospheres absolute and the contact time of reactantsand the first catalyst composition is in the range of about 0.5 to 100seconds.
 6. The process according to claim 1, wherein the reactants instep (a) consist of acetic acid and hydrogen with a molar ratio in therange of about 1:20 to 1:2, the temperature is in the range of about300° C. to 350° C., and the pressure is in the range of about 1 to 30atmospheres absolute and the contact time of reactants and the firstcatalyst composition is in the range of about 0.5 to 100 seconds.
 7. Theprocess according to claim 1, wherein the third catalyst in step (d)comprises palladium.
 8. The process according to claim 7, wherein thethird catalyst in step (d) further comprises gold and potassium acetate.9. The process according to claim 7, wherein the palladium is supportedon a catalyst support selected from the group consisting of silica,alumina, silica-alumina, titania and zirconia.
 10. The process accordingto claim 1, wherein the mole ratio of ethylene to molecular oxygen isabout 4:1 or less.
 11. The process according to claim 1, wherein in step(c) molecular oxygen is added in the form of air.
 12. The processaccording to claim 1, wherein said first catalyst composition isselected from the group consisting of copper supported on iron oxide andcopper-aluminum catalyst.
 13. The process according to claim 12, whereinthe first catalyst composition has a copper loading in the range ofabout 3 weight percent to about 10 weight percent.
 14. The processaccording to claim 1, wherein the first and second reaction zonescomprise respectively a first layer of the first catalytic compositionand a second layer of the second catalytic composition in a fixed bed.15. The process according to claim 1, wherein the first and secondreaction zones are in separate vessels.
 16. The process according toclaim 1, wherein the selectivity to ethylene based on acetic acidconsumed is at least about 80%.